“Fermi Bubbles,” which might appear as a void in visible light in spiral galaxies. is the term used by Richard Carrigan at the Fermi National Accelerator Laboratory in his work on the search for cosmic-scale artifacts like Dyson spheres or Kardashev civilizations. A Fermi bubble would grow as the civilization creating it colonized space, according to Carrigan.

As Carl Sagan observed, the time to colonize an individual system is small compared to the travel time between stars. A civilization, believes Carrigan, could engulf its galaxy on a time scale comparable to the rotation period of the galaxy, or every 225–250 million years, and perhaps shorter.

Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization.

This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. The constraints of the anthropic principle, for example, would have to be loosened if a different type of intelligence was discovered elsewhere.